PLL sonic bilge pump switch

Abstract

An apparatus for activating and deactivating a bilge pump in a marine vessel in response to the presence or absence of water or other fluid in the bilge area wherein a pair of acoustic transducers are mounted in proximate and opposed relationship to one another such that a first transducer, the generator transducer, transmits acoustic waves to a second transducer, the receiver transducer, across a designated narrow channel. The apparatus operates on the principle that acoustic waves transmit greater energy in a dense transmission medium such as water or other liquid. The sensitivity of the transducer pair and its associated electronic circuitry is adjusted such that the transmitted acoustic signal is detected at the receiver transducer when the signal is transmitted through liquid and the signal fails to reach a detectable level at the receiver transducer when the signal is transmitted through air. The detected signal triggers electronic circuitry operating a relay coil which switches power to the bilge pump. The circuitry of the present invention also incorporates a time delay circuit creating a damping effect on the switching control to prevent switching during sudden movement of water.

What is claimed is: 
     
       1. An apparatus for activating and deactivating a bilge pump in response to the detection of the presence or absence of fluid in a bilge hold, comprising: oscillator means for producing a periodic signal having a predetermined frequency to energize a first transducer means;   first transducer means for converting said periodic signal to an acoustic signal and operative to transmit said acoustic signal;   second transducer means for receiving said acoustic signal and operative to convert said acoustic signal to an electrical signal upon the condition that the magnitude of said acoustic signal exceeds a predetermined magnitude, said predetermined magnitude indicating the presence of fluid between said first and second transducer means;   detector means coupled to said second transducer means and said oscillator means, for detecting whether said received acoustic signal is of the same frequency as said predetermined frequency, and for producing an electrical trigger signal in response thereto; and   switch means coupled to said detector means for receiving said electrical trigger signal and connecting a bilge pump to a voltage source.   
     
     
       2. The apparatus of claim 1, further including activation circuit means coupled to said detector means, for receiving said electrical trigger signal and energizing said switch means, connecting said bilge pump to the voltage source. 
     
     
       3. The apparatus of claim 2 further including voltage regulator means for producing a voltage signal; and means, coupled to said voltage signal for generating a predetermined reference voltage.   
     
     
       4. The apparatus of claim 3, wherein said activation circuit comprises: buffer means responsive to said electrical trigger signal and operative to produce a time delayed output signal; and   comparator means coupled to said buffer means for comparing said time delayed output signal to said predetermined reference voltage and energizing said switch means.   
     
     
       5. The apparatus of claim 1 including a waterproof housing means, wherein said housing means comprises a unitary structure for mounting said first and second transducer means in proximate and opposing relation to one another and wherein the remainder of said apparatus is enclosed within said waterproof housing means. 
     
     
       6. The housing means of claim 5, further including an independent mounting plate for securing said housing means on said mounting plate in a location within a bilge hold of a marine vessel. 
     
     
       7. The housing means of claim 5, wherein only said first and second transducer means are mounted on said housing means and the remainder of said apparatus is located in a physically independent unit which is electronically coupled to said first and second transducer means. 
     
     
       8. The apparatus of claim 1, further including a housing for fixturing said first and second transducer means in facing relationship across a gap open to the bilge. 
     
     
       9. The apparatus of claim 1, wherein said detector means is a phased-locked loop detector. 
     
     
       10. The apparatus of claim 1, wherein said first and second transducer means comprise a piezo-electric material.